The Christian owners of a bakery are to begin their appeal against a court ruling which found they discriminated against a gay man.
A judge at Belfast County Court said Ashers Baking Company, run by the McArthur family, acted unlawfully by declining an order from gay rights activist Gareth Lee.
Mr Lee, a member of the LGBT advocacy group Queer Space, had wanted a cake featuring Sesame Street puppets Bert and Ernie with the slogan Support Gay Marriage for a private function marking International Day Against Homophobia in May 2014.
He paid in full when placing the order at Ashers' Belfast branch, but said he was stunned when - two days later - the company phoned to say it could not be processed.
The high profile case was heard over three days last March.
Delivering her reserved judgment two months later, District Judge Isobel Brownlie found Ashers directly discriminated against Mr Lee who had been treated "less favourably", contrary to the law.
Ordering the bakers to pay agreed damages of £500, the judge said religious beliefs could not dictate the law.
The Northern Ireland Equality Commission, which monitors compliance with the region's anti-discrimination laws, took the landmark legal action on behalf of Mr Lee.
The image Ashers were asked to put on the cake
The publicly funded watchdog had initially asked for the bakery on Belfast's Royal Avenue to acknowledge it had breached legislation and offer "modest" damages but proceeded with the court challenge when the firm refused.
Ashers, which employs 80 staff in nine branches and delivers across the UK and Ireland, was supported by the Christian Institute - which organised public meetings and garnered financial backing.
In evidence, Mr Lee claimed the company's refusal to make the cake left him feeling like a "lesser person".
Karen McArthur, a director at Ashers, said she had accepted the order to avoid a confrontation or to avoid embarrassment in the shop, but as a born again Christian "knew in her heart" it could not be fulfilled.
General manager, Daniel McArthur, 26, said the family could not compromise their deeply held religious beliefs despite the legal ramifications.
The father of two said the legal wrangle had strengthened his faith in God.
He said: "It was clear we did not hate anyone. We didn't want to discriminate against anyone. We did what we did because of our Christian beliefs.
"It's done out of love for God, to obey him.
"Our hope and prayer would be that an appeal will allow us and other Christians to live out their faith in Jesus Christ in every part of their lives, including their workplace."
The issue of gay marriage has split public opinion in Northern Ireland.
In 2005, the region became the first in the UK to allow same-sex civil partnerships but the devolved Stormont Assembly has repeatedly refused to change the law around marriage.
Following last May's referendum in the Republic, it is now the only part of the UK or Ireland to deny civil marriage to same sex couples.
Two same sex couples are now seeking to challenge the ban through a judicial review in the courts.
Gareth Lee arrived at court accompanied by the Equality Commission's chief commissioner, Dr Michael Wardlow.
Mr Wardlow said if the ruling was overturned it would raise "all sorts of issues about the protection of minorities".
"There has been a lot of misinformation in the media that somehow this about closing down religious expression, that faith has to be left at the door of the workplace and that is not true," he said.
"Religious freedom is enshrined in the legislation. The problem is although freedom to believe is absolute, freedom to express that belief is always limited, because if by expressing that belief you discriminate against others then the law must intervene.
"So this is not simply about some form of religious intolerance or closing down of Christian expression because in all of this the other person who has a right in this, who seems to have been forgotten, is Gareth.
"So I would like this to be seen for what it is - this is about if you enter into the public domain and choose to trade as a commercial enterprise you are ruled by the laws of the land."
